High resistance polyaniline useful in high efficiency pixellated polymer electronic displays

ABSTRACT

A film including polyaniline in the emeraldine salt form (PANI) and poly(2-acrylamido-2 methyl-1-propanesulfonic acid) (PAAMPSA) as a counterion and optionally a water-soluble host polymer, the film is useful in an electronic device such as pixellated displays.

FIELD OF INVENTION

[0001] This invention relates to a formulation of high resistivitypolyaniline in the emeraldine salt form for use in high efficiencypixelated polymer electronic devices, such as emissive displays. Thehigh resistivity layer provides excellent hole injection, preventselectrical shorts, enhances the device lifetime and avoids inter-pixelcurrent leakage.

BACKGROUND OF THE INVENTION

[0002] Light emitting diodes (LEDs) fabricated with conjugated organicpolymer layers have attracted attention due to their potential for usein display technology.

[0003] In the field of organic polymer-based LEDs it has been taught inthe art to employ a relatively high work function metal as the anode;said high work function anode serving to inject holes into the otherwisefilled π-band of the semiconducting, luminescent polymer. Relatively lowwork function metals are preferred as the cathode material; said lowwork function cathode serving to inject electrons into the otherwiseempty π*-band of the semiconducting, luminescent polymer. The holesinjected at the anode and the electrons injected at the cathoderecombine radiatively within the active layer and light is emitted. Thecriteria for suitable electrodes are described in detail by I. D.Parker, J. Appl. Phys, 75, 1656 (1994).

[0004] Suitable relatively high work function metals for use as anodematerials are transparent conducting thin films of indium/tin-oxide (H.Burroughs, D. D. C. Bradley, A. R. Brown, R. N. Marks, K. Mackay, R. H.Friend, P. L. Burns, and A. B. Holmes, Nature 347, 539 (1990); D. Braunand A. J. Heeger, Appl Phys. Lett. 58, 1982 (1991)).

[0005] Alternatively, thin films of conducting polymers such aspolyaniline (see P. Snuth, A. J. Heeger, Y. Cao, J. Chiang and A.Andreatta, U.S. Pat. No. 5,470,505) can be used as demonstrated by G.Gustafsson, Y. Cao, G. M. Treacy, F. Klavetter, N. Colaneri, and A. J.Heeger, Nature, 357, 477 (1992), by Y. Yang and A. J. Heeger, Appl.Phys. Lett 64, 1245 (1994) and U.S. Pat. No. 5,723,873, by Y. Yang, E.Westerweele, C. Zhang, P. Smith and A J. Heeger, J. Appl. Phys. 77, 694(1995), by J. Gao, A. J. Heeger, J. Y Lee and C. Y Kim, Synth. Met.,82,221 (1996) and by Y. Cao, G. Yu, C. Zhang, R. Menon and A. J. Heeger,Appl. Phys. Lett. 70, 3191, (1997). Thin films of indium/tin-oxide andthin films of polyaniline in the emeraldine salt form with certaincounterions (PANI(ES)) are preferred because, as transparent electrodes,both enable the emitted light from the LED to radiate from the device inuseful levels. Using a layer of PANI(ES), or blends comprising PANI(ES),directly between the ITO and the light-emitting polymer layer, C. Zhang,G. Yu and Y. Cao (U.S. Pat. No. 5,798,170) demonstrated polymer LEDshaving bilayer electrodes with long operating lifetimes.

[0006] Despite the advantages of using PANI(ES) in a bilayer electrodeof polymer LEDs (as described in U.S. Pat. No. 5,798,170), the lowelectrical resisitivity typical of PANI(ES) inhibits the use of PANI(ES)in pixellated displays. For use in pixellated displays, the PANI(ES)layer should have a high electrical sheet resistance, otherwise lateralconduction causes cross-talk between neighboring pixels. The resultinginter-pixel current leakage significantly reduces the power efficiencyand limits both the resolution and the clarity of the display.

[0007] Making the PANI sheet resistance higher in a bilayer electrode byreducing the film thickness is not a good option since thinner filmsgive lower manufacturing yield caused by the formation of electricalshorts. This is demonstrated clearly in FIG. 1, which shows the fractionof “leaky” pixels in a 96×64 array vs. thickness of the PANI(ES)polyblend layer. Thus, to avoid shorts, it is necessary to use arelatively thick PANI(ES) layer with thickness of about 200 nm.

[0008] With a film thickness of 200 nm or greater, the electricalresistivity of the PANI(ES) layer should be greater than or equal to 10⁴ohm-cm to avoid crosstalk and inter-pixel current leakage. Values inexcess of 10⁵ ohm-cm are preferred. Even at 10⁵ ohm-cm, there is someresidual current leakage and consequently some reduction in deviceefficiency. Thus, values of approximately 10⁶ ohm-cm are even morepreferred. Values greater than 10⁷ ohm-cm will lead to a significantvoltage drop across the injection/buffer layer and therefore should beavoided. To achieve high resistivity PANI(ES) materials withresitivities in the desired range requires reformulation of thePANI(ES).

[0009] Thus, there is a need for a formulation of high resistivelyPANI(ES) for use in high efficiency pixellated polymer emissivedisplays.

SUMMARY OF THE INVENTION

[0010] The present invention is directed to a PANI-PAAMPSA filmcomprising polyaniline in the emeraldine salt form (PANI) withpoly(2-acrylamido-2 methyl-1-propanesulfonic acid) (PAAMPSA) as thecouterion, and a method of forming the film by casting. In a preferredembodment, the PANI-PAAMPSA film is a blend of PANI-PAAMPSA with atleast one water-soluble host polymer. The invention is also directed toan electronic device comprising the PAM-PAAMPSA film. Further, theinvention is directed to a light-emitting diode including thePANI-PAAMPSA film. In a preferred embodiment, the film of the presentinvention is disposed adjacent to the high work function electrode. Inanother preferred embodiment, in the light-emitting polymer device, thePANI-PAAMPSA layer is disposed between the light-emitting layer and thehigh work function electrode.

[0011] As used herein, the term “adjacent” is used to indicate that thePANI-PAAMPSA layer is closer to the high work function electrode, whencompared to its distance to the low work function electrode, but thatthere may or may not be another layer present between the PANI-PAAMPSAlayer and the high work function electrode. As used herein the term“between” also does not preclude the possibility that a component layerother than the PANI-PAAMPSA layer may be present between the high workfunction electrode and the light-emitting polymer.

[0012] As used herein, the terms “conductivity” and “bulk conductivity”are used interchangeably, the value of which is provided in the unit ofSiemens per centimeter (S/cm). In addition, the terms “surfaceresistivity” and “sheet resistance” are used interchangeably to refer tothe resistance value that is a function of sheet thickness for a givenmaterial, the value of which is provided in the unit of ohm per square(ohm/sq). Also, the terms “bulk resistivity” and “electricalresistivity” are used interchangeably to refer to the resistivity thatis a basic property of a specific materials (i.e., does not change withthe dimension of the substance), the value of which provided in the unitof ohm-centimeter (ohm-cm). Electrical resistivity value is the inversevalue of conductivity.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a graph which shows the fraction of “leaky pixels (in a96×64 array) vs. thickness of the known PANI(ES) layer.

[0014]FIG. 2 is a projected schematic diagram of the component layers ofa passively addressed, pixelated, polymer LED display.

[0015]FIG. 3 is a graph which shows the dependence of the conductivityof PANI-PAAMPSA polyblends on PANI-PAAMPSA content.

[0016]FIG. 4 is a graph which shows the light output and externalquantum efficiency for a device fabricated with the PANI-PAAMPSA layer.

[0017]FIG. 5 is a graph which shows the stress induced degradation of adevice with PANI-PAAMPSA layer at 85° C.

[0018]FIG. 6 is a graph which shows the stress induced degradation ofdevices with PANI-PAAMPSA layer at room temperature.

[0019]FIG. 7 is a graph which shows the stress induced degradation of adevice with a PANI-PAAMPSA blend (Example 9) as the layer; the data wereobtained with the device at 70° C.

[0020]FIG. 8 shows photographs of three passively addressed displays(96×64) that were identical in every respect except that the display inFIG. 8a had a low resistance PEDT layer (resistivity is ˜200 ohm-cm),while the display in FIG. 8b had a PANI-PAAMPSA polyblend layer,(resistivity is ˜4,000 ohm-cm), and the display in FIG. 8c a higherresistance PANI-PAAMPSA polyblend layer (resistivity is ˜50,000 ohm-cm).

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0021] The invention is based on the development of a formulation ofemeraldine salt of polyaniline, PANI(ES), more particularly,PANI-PAAMPSA formulations, which leads to high resistivity PANI(ES)films useful in high efficiency electronic devices, such as pixelatedpolymer emissive displays. In addition, a method has been developed fordepositing a thin transparent film of high resisitivty PANI(ES) from anaqueous dispersion onto a substrate, such as either a pre-patternedITO-on-glass substrates or pre-patterned ITO-on-plastic substrates. Byusing the high resistivity PANI(ES) layer described in this invention,long operating life is enabled in high information content displayswithout the need for registered patterning of the PANI(ES) layer.

[0022] While the formulation of the invention is useful in non-pixelatedas well as pixelated electronic devices, the advantages are especiallyapplicable in pixelated devices, such as, for example anelectroluminescent display.

[0023] Device Configuration:

[0024]FIG. 2 shows a polymer emissive device 10 having 156 (12×13)pixels. As shown in FIG. 2, each individual pixel of the device 10includes an electron injecting (electrode) contact 20 made from arelatively low work function metal as one electrode on a emissive film30 deposited on a glass or polymeric film substrate 40, which has beenpartially coated with a layer 50 of transparent conducting material withhigher work function (high ionization potential) to serve as the second(transparent) electron-withdrawing (anode) electrode. The componentlayers 20, 30, 40, 50 are common components in a known polymer LEDs (D.Braun and A. J. Heeger, Appl. Phys. Lett. 58, 1982 (1991). In accordancewith this invention, a layer 60 comprising high resistivity PANI(ES) isinterposed between the emissive layer 30 and the high work functionelectrode 50. Electrode 20 is electrically connected to contact pads 80,and electrode 50 is electrically connected to contact pads 82. Thelayers 20, 30, 40, 50, and 60 are then isolated from the environment bya hermetic seal layer 70. Upon application of electricity via contactpads 80, 82, which pads are outside of the hermetic seal 70, light isemitted from the device in the direction shown by arrow 90.

[0025] The PANI-PAAMPSA Layer (60)

[0026] In accordance to the present invention layer 60 includes aPANI-PAAMPSA film containing polyaniline in the emeraldine salt formwith poly(2-acrylamido-2 methyl-1-propanesulfonic acid) as a counterion.

[0027] The PANI-PAAMPSA complex of the invention can be prepared by anyknown method for forming PANI(ES) complexes, including, for example themethods described in Y. Cao et al., Polymer, 30 (1989) 2305; and StevenP. Armes and Mahmoud Aldissi, J. Chem. Soc., Chem. Commun. 1989, 88. Ina preferred embodiment, aniline is dissolved in a suitable anilinesolvent. The PAAMPSA can then be added into aniline in solvent to getaniline-PAAMPSA salt which is soluble in water. Once aniline iscompletely dissolved into water, reaction vessel can be placed intothermostart in order to regulate the reaction temperature. Althoughlower temperature can be used the typical polymerization temperature canbe maintained between 0° C. and 25° C. Lower temperature givespolyaniline with high molecular weight, but reaction time would belonger. A strong oxidizer can then be added to the solution to intiatepolymerization. After polymerization is completed, the emulsion ofPANI-PAAMPSA can be separated from reaction mixture by adding acetone.The resulting PANI-PAAMPSA can be purified at least twice by dispersioninto water and then precipitation from mixture by acetone, to removeunreacting aniline monomer and oxidants and byproduct of polymerizationwere eliminated from PANI-PAAMPSA.

[0028] Suitable aniline solvents are water-soluble solvents that do notadversely affect the desired chemical reaction and include, for example,water, mixture of water with at least one water-soluble alcohols,mixture of water with tetrahydrofuran (THF), mixture of water withdimethyl sulfoxide (DMSO), or mixture of water withN,N′-dimethylformamide (DMF) or mixture of water with other solventsmixable with water.

[0029] Suitable oxidizer useful to form the PANI-PAAMPSA complexinclude, for example, ammonium persulfate, potasium dichromate andferric chloride and hydrogen peroxides.

[0030] The resistivity of layer 60 can be affected by, for example, theratio of aniline to PAAMPSA used to form the PANI-PAAMPSA complex, thethickness of layer 60, as well as the presence of other components inlayer 60.

[0031] In a preferred embodiment, the weight ratio of aniline to PAAMPSAused to form the PANI-PAAMPSA complex is from 2:1 to 0.5:1. Morepreferably, the aniline to PAAMPSA weight ratio is about 1:1. We havefound that, with decreasing aniline to PAAMPSA ratio, the conductivityand dispersion of the PANI(ES) also decrease.

[0032] Depending on the amount and type of additional components inlayer 60, typical thicknesses for layer 60 can range from about 100 Å upto about 2500 Å.

[0033] In one embodiment the resistivity of layer 60 is furthercontrolled by blending the PANI-PAAMPSA in one or more water dispersibleand/or water-solublewater-soluble host polymer. Suitable host polymersinclude, but are not limited to, polyacrylamide (PAM), PAAMPSA,poly(acrylic acid) (PAA), poly(styrenesulfonic acid), poly(vinylpyrrolidone)(PVPd), acrylamide copolymers, cellulose derivatives,carboxyvinyl polymer, poly(ethylene glycols), poly(ethylene oxide)(PEO), poly(vinyl alcohol) (PVA), poly(vinyl methyl ether), polyamine,polyimines, polyvinylpyridines, polysaccharide, and polyurethanedispersion, and combinations thereof.

[0034] The desired amount of such host polymer(s) to form a blend orpolyblend in layer 60 depends upon the desired resistivity value of thefinal film and processing considerations, including the molecular weightof the host polymer and the desired viscosity of the blend or polyblend.In one preferred embodiment, the weight ratio of PANI(ES)-PAAMSA complexto host polymer(s) in layer 60 is from 1:0.1 to 1:9.

[0035] Where the PANI-PAAMPSA forms a blend with one or more hostpolymer(s), the following procedure can be used to prepare the blend orpolyblend: the PANI(ES)-PAAMPSA is dissolved in a suitable water-solublesolvent to form a first solution, the host polymer(s) is/are dissolvedin a suitable water-soluble solvent to form a second solution, and ablend solution is formed by combining the first and second solutions inthe desired ratio.

[0036] Suitable water-soluble solvents for the first and secondsolutions in the blend-making process may be the same or different fromthe aniline solvents, and may be, for example, and include, for example,water, mixture of water with at least one water-soluble alcohols,mixture of water with tetrahydrofuran (THF), mixture of water withdimethyl sulfoxide (DMSO), or mixture of water withN,N′-dimethylformamide (DMF) or mixture of water with other solventsmixable with water. In a preferred embodiment, the PANI-PAAMPSA layer 60is useful in a non-pixelated electronic device and has an electricalresistivity of greater than 10² ohm-cm. In another preferred embodiment,layer 60 includes a blend or polyblend of PANI-PAAMPSA with at least onewater-solublewater-soluble or water dispersible host polymer(s).and hasan electrical resistivity greater than 10⁴ ohm-cm, more preferably 10⁵ohm-cm, even more preferably greater than 10⁶ ohm-cm. Such blends andpolyblends of PANI-PAAMPSA are useful in a pixellated electronic device.

[0037] While layer 60 in the illustrated device 10 is un-patterned, itis understood that the PANI-PAAMPSA film of the present invention mayalso be patterned.

[0038] The High Work Function Electrode (50)

[0039] Other organic or inorganic materials having electrical workfunctions similar to ITO may be used in component 50, including, forexample, mixed oxides of metals from Group IIA (Be, Mg, Ca, Sr, Ba, Ra),other metals from Groups IIIA (B, al, Ga, Tl) and metals from Group IVA(C, Si, Ge, Sn, Pb). Examples of suitable organic materials useful inplace of ITO include polyaniline and poly(3,4-ethylenedioxythiophene)(PEDT).

[0040] In a pixellated electroluminescent device, the surface electricalresistance of layer 50 is preferably less than about 100 ohms/square. Assuch, the typical thicknesses for layer 50 can range from about 100 Å upto about 2500 Å.

[0041] In the illustrated embodiment, the component layers 50 and 60and, when present, the substrate 40, can be “transparent” or“semitransparent” so as to permit the emitted light to pass out thoughthese components. A “transparent” or “semitransparent” material is amaterial that passes at least a fraction of the light impinged upon it,such as at least about 10% and preferably at least 20% of the lightemitted by the light-emitting layer 30 at the wave length of thisemission. In an alternative embodiment (not shown) the low work functionelectrode 20 is transparent or semitransparent, while the components 40,50 and/or 60 are opaque.

[0042] The Light-Emitting Layer (30)

[0043] Layer 30 can include any organic luminescent material, includingpolymer and/or molecular ligh-emitting materials.

[0044] Among the promising materials for use as active layers in polymerLEDs are poly (phenylene vinylene), PPV, and soluble derivatives of PPVsuch as, for example,poly(2-methyoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene), MEH-PPV,a semiconducting polymer with an energy gap Eg of approximately 2.1 eV.This material is described in more detail in U.S. Pat. No. 5,189,136.Other suitable polymers include, for example, thepoly(3-alkylthiophenes) as described by D. Braun, G. Gustatsson, D.McBranch and A. J. Heeger, J. Appl. Phys. 72, 564 (1992) and relatedderivatives as described by M. Berggren, O. Inganas, G. GustaLsson, J.Rasmusson, M. R. Andersson, T. Hjertberg and O. Wennerstrom;poly(para-phenylene) as described by G. Grem, G. Leditzlcy, B. Ullrich,and G. Leising, Adv. Mater 4, 36 (1992), and its soluble derivatives asdescribed by Z. Yang, I. Sokolik, F. E. Karasz in Macromolecules, 26,1188 (1993), polyquinoline as described by I. D. Parker, Q. Pei and M.Marrocco, Appl. Phys. Lett. 65, 1272 (1994). Blends of conjugatedsemiconducting polymers in non-conjugated host polymers are also usefulas the active layers in polymer LEDs as described by C. Zhang, H. vonSeggem, K Pakbaz, B. Krsabel, H. W. Schmidt and A. J. Heeger, Synth.Met., 62, 35 (1994). Also useful are blends comprising two or moreconjugated polymers as described by H. Nishino, G. Yu, T-A Chen, R. D.Rieke and A. J. Heeger, Synth. Met., 48, 243 (1995). The use ofconjugated copolymers in electroluminescent application is described byA. Holmes, D. D. Bradley, R H. Friend, A. Kraft, P. Burn and A. Brown inU.S. Pat. No. 5,401,827. Generally, materials for use as active layersin polymer LEDs include semiconducting conjugated polymers, morespecifically semiconducting conjugated polymers which exhibitphotoluminescence, and still more specifically semiconducting conjugatedpolymers which exhibit photoluminescence and which are soluble andprocessible from solution into uniform thin films.

[0045] In another embodiment, the light-emissive layer 30 may includeorganic molecules such anthracene, thiadiazole derivatives, and coumarinderivatives are known to show electroluminescence. In addition,complexes of 8-hydroxyquinolate with trivalent metal ions, particularlyaluminum, have been extensively used as electroluminescent components,as has been disclosed in, for example, Tang et al., U.S. Pat. No.5,552,678. In particular, fac-tris(2-phenylpyridine) iridium can be usedas the active component in organic light-emitting devices. (Burroughesand Thompson, Appl. Phys. Lett. 1999, 75, 4.) The performance ismaximized when the iridium compound is present in a host conductivematerial. Thompson has further reported devices in which the activelayer is poly(N-vinyl carbazole) doped withfac-tris[2-(4′,5′-difluorophenyl)pyridine-C′²,N]iridium(III). (PolymerPreprints 2000, 41(1), 770.)

[0046] The Low Work function Electrode (20)

[0047] Suitable relatively low work function metals for use as cathodematerials are the alkaline earth metals such as calcium, barium,strontium and rare earth metals such as ytterbium. Alloys of low workfunction metals, such as for example alloys of magnesium in silver andalloys of lithium in aluminum, are also known in prior art (U.S. Pat.Nos. 5,047,687; 5,059,862 and 5,408,109). The thickness of the electroninjection cathode layer has ranged from 200-5000 Å as demonstrated inthe prior art (U.S. Pat. Nos. 5,151,629, 5,247,190, 5,317,169 and J.Kido, H. Shionoya, K. Nagai Appl. Phys. Lett., 67(1995)2281). A lowerlimit of 200-500 Angstrom units (Å) is preferred in order to form acontinuous film (full coverage) for cathode layer (U.S. Pat. No.5,512,654; J. C. Scott, J. H. KauLman, P. J. Brock, R DiPietro, J. Salemand J. A. Goitia, J. Appl. Phys., 79(1996)2745; I. D. Parker, H. H. Kim,Appl. Phys. Lett., 64(1994) 1774).

[0048] Electron-injecting cathodes comprising ultra-thin layer alkalineearth metals, calcium, strontium and barium, have been described forpolymer light emitting diodes with high brightness and high efficiency.Compared to conventional cathodes fabricated from the same metals (andother low work function metals) as films with thickness greater than200Å, cathodes comprising ultra-thin layer alkaline earth metals with athickness less than 100 Å provide significant improvements in stabilityand operating life to polymer light emitting diodes (Y. Cao and G. Yu,PCT WO 98/57381). Electron-injecting cathodes comprising thinmetal-oxide layers have also been described by Y. Cao in PCT WO 00/22683for use in polymer light emitting diodes.

[0049] By using the high resistivity PANI(ES) layer described in thisinvention, long operating life is enabled in high information contentdisplays without the need for registered patterning of the PANI(ES)layer.

[0050] While the illustrated device 10 is described as useful for alight-emitting display, it is understood that the present PANI-PAAMPSAmaterial is also useful in other electronic devices, including, forexample, photosensors, photodetectors, microcavity, electrically pumpedpolymer and organic lasers, as well as organic and polymer FETs (fieldeffect transistors).

[0051] Contac Pads (80 82)

[0052] Any contact pads 80, 82 useful to connect the electrode of thedisplay 10 to the power source (not shown) can be used, including, forexample, conductive metals such as gold (Au), silver (Ag), nickel (Ni),copper (Cu) or aluminum (Al).

[0053] Preferably, contact pads 80, 82 have a height (not shown)projected beyond the thickness of the high work function electrode lines50 below the total thickness of layer.

[0054] Preferably, the dimensions of layers—30, 50, and 60 are such thatcontacts pads 80 are positioned on a section of the substrate 40 notcovered by layers 30, 60 and 70. In addition, the dimensions of layer20, 30, 50, and 60 are such that the entire length and width electrodelines 20 and electrode lines 50 have at least one layer 30, 60intervening between the electrodes 20, 50, while electrical connectioncan be made between electrode 20 and contact pads 80.

[0055] Fabrication Method

[0056] The various elements other than the PANI-PAAMPSA layer of thedevices of the present invention may be fabricated by any of thetechniques well known in the art, such as solution casting, vapordeposition, screen printing, contact printing, sputtering, evaporation,precursor polymer processing, melt-processing, and the like, or anycombination thereof.

[0057] The PANI-PAAMPSA film layer of the present invention is providedusing any known casting process, such as solution casting and dropcasting, screen printing, contact printing and the like, or anycombination thereof. An aqueous solution or aqueous dispersioncontaining PANI-PAAMPSA complex or a blend/polyblend of at least onehost polymer and PANI-PAAMPSA complex can be made with any suitablesolvent. Suitable PANI-PAAMPSA solvent for the casting process arewater-soluble and include, for example, water, mixtures of water andwater-soluble alcohols, mixture of water with THF, mixture of water withDMSO, mixture of water with DMF, or mixture of water with other solventsmixable with water. Although not necessary, the same aniline solventused to form PANI-PAAMPSA complex can be used to cast the PANI-PAAMPSAfilm.

[0058] As is known in the art, the thickness of the film can be affectedby, among others the viscosity, solid content, and chemical compositionof the aqueous dispersion or aqueous solution. A typical viscosity rangeis from 50 centipose (cps) to 200 cps. As such, the typical weight ratioof polymer material (i.e., PANI-PAAMPSA, and, when present, the at leastone host polymers) to solvent is 0.5% (w/w) to 5% (w/w). Process aidssuch as viscosity modifiers may also be added to the aqueousdispersion/solution for casting.

[0059] Casting can be performed at room temperature, although lower orelevated temperatures known in the art can be used.

[0060] A thin film can be then be casted from the aqueous solution oraqueous dispersion onto a support such as an thin layer of anodematerial that is optionally on a substrate of glass, plastic, ceramic,or silicon, or flexible support.

[0061] The present invention provides a method for obtaining longoperating life by using an anode coated with a formulation comprisingPANI-PAAMPSA.

[0062] Unless otherwise specified all percentages are percentages byweight.

EXAMPLES Example 1

[0063] PANI-PAAMPSA was prepared using a procedure similar to thatdescribed in the reference Y. Cao, et al, Polymer, 30(1989) 2305, morespecifically, as described below. HCl in this reference was replaced bypoly(2-acrylamido-2-methyl-1-propanesulfonic acid (PAAMPSA) (availablefrom Aldrich, Milwaukee, Wis. 53201).

[0064] The emeraldine salt (ES) form was verified by the typical greencolor. First, 30.5 g (0.022 mole) of 15% PAAMPSA in water (Aldrich) wasdiluted to 2.3% by adding 170 ml water. While stirring, 2.2 g (0.022M)aniline was added into the PAAMPSA solution. Then, 2.01 g (0.0088M) ofammonium persulfate in 10 ml water was added slowly into theaniline/PAAMPSA solution under vigorous stirring. The reaction mixturewas stirred for 24 hours at room temperature. To precipitate theproduct, PANI-PAAMPSA, 1000 ml of acetone was added into reactionmixture. Most of acetone/water was decanted and then the PANI-PAAMPSAprecipitate was filtered. The resulting gum-like product was washedseveral times by acetone and dried at 40° C. under dynamic vacuum for 24hours.

[0065] This Example demonstrates the direct synthesis of PANI-PAAMPSA.

Example 2

[0066] One gram (1.0 g) of the PANI-PAAMPSA powder as prepared inExample 1 was mixed with 100 g of deionized water in a plastic bottle.The mixture was rotated at room temperature for 48 hours. Thesolutions/dispersions were then filtered through 0.45 μm polypropylenefilters. Different concentrations of PANI-PAAMPSA in water are routinelyprepared by changing the quantity of PANI-PAAMPSA mixed into the water.

[0067] This Example demonstrates that PANI-PAAMPSA can bedissolved/dispersed in water and subsequently filtered through a 0.45 μmfilter.

Example 3

[0068] A PANI-PAAMPSA film was drop-casted from 1% w/w)solution/dispersion in water. The film thickness was measured to be 650nm by a surface profilometer (Alpha-Step 500) (available fromKLA-Tencor, San Jose, Calif. 95134). Using standard X-ray equipment, awide-angle diffraction diagram (WAXD) was taken on the PANI-PAAMPSAfilm. The diffraction pattern showed no characteristic diffractionpeaks; the data indicated that the film was amorphous.

[0069] This Example demonstrates that the PANI-PAAMPSA film cast fromwater is amorphous (crystallinity less than 10%).

Example 4

[0070] Four grams (4.0 g) of polyacrylamide (PAM) (M.W.5,000,000-6,000,000, available from Polysciences (Warrinton, Pa. 18976)was mixed with 400 ml deionized water in a plastic bottle. The mixturewas rotated at room temperature for at least 48 hours. Thesolution/dispersion was then filtered through 1 μm polypropylenefilters. Different concentrations of PAM are routinely prepared bychanging the quantity of PAM dissolved.

[0071] This Example demonstrates that PAM can be dissolved/dispersed inwater and subsequently filtered through a 1 μm filter.

Example 5

[0072] Ten grams (10 g) of the PANI-PAAMPSA solution as prepared inExample 2 was mixed with 20 g of 1% (w/w) PAM solution as prepared inExample 4 (mixed at room temperature for 24 hours). The solution wasthen filtered through 0.45 μm polypropylene filters. The PANI-PAAMPSA toPAM ratio was 1:2 in the blend solution. Different blend ratios of thePANI-PAAMPSA/PAM solutions were prepared by changing the concentrationsof PANI-PAAMPSA and PAM in the starting solutions including thefollowing: PANI-PAAMPSA/PAM (w/w) at 2/1, and 1/1.

[0073] This Example demonstrates that PANI-PAAMPSA/PAM blends can beprepared with a range of PAM concentrations, that these blends can bedissolved/dispersed in water and that they can be filtered through a0.45 μm.

Example 6

[0074] Example 5 was repeated, but PAAMPSA was used instead of PAM. Theblend ratio of PANI-PAAMPSA/PAAMPSA (w/w) was, respectively, 1/0.1,1/0.3, 1/0.5, 1/1 and 1/2.

[0075] This Example demonstrates that PANI-PAAMPSA/PAAMPSA blends can beprepared with a range of PAAMPSA concentrations, that these blends canbe dissolved/dispersed in water and that they can be filtered through a0.45 μm filter.

Example 7

[0076] Example 5 was repeated, but PEO was used instead of PAM. Theblend ratio of PANI-PAAMPSA/PEO (w/w) was 1/1.

Example 8

[0077] Glass substrates were prepared with patterned ITO electrodes.Using the blend solutions as prepared in Examples 5, 6 and 7,polyaniline blend layers were spin-cast on top of the patternedsubstrates and thereafter, baked at 90° C. in a vacuum oven for 0.5hour. The resistance between ITO electrodes was measured using a highresistance Keithley 487 Picoammeter, from Keithley Instruments Inc.,(Cleveland, Ohio 44139). Table 1 shows the conductivity ofPANI(ES)-blend films with different blend compositions. As can be seenfrom Table, the conductivity can be controlled over a wide range.

[0078] This Example demonstrates that the PANI-PAAMPSA blends can beprepared with bulk conductivities less than 10⁻⁴ S/cm, and even lessthan 10⁻⁵ S/cm; i.e. sufficiently low that interpixel current leakagecan be limited without need for patterning the PANI-PAAMPSA blend film.TABLE 1 Surface resistivity and bulk conductivity of PANI-PAAMPSA blendsElectrical host polymer Thick- A/B Surface Con- Resistivity (B) nessratio* Resistance ductivity (ohm- Blend (if present) (Å) (w/w) (ohm/sq)(S/cm) cm)** 100 none 350 1.2 × 10⁸ 2.3 × 10⁻³ 4.3 × 10² 101 none 2002.2 × 10⁸ 2.2 × 10⁻³ 4.5 × 10² 102 PAM 300 2/1 2.3 × 10⁹ 1.5 × 10⁻⁴ 6.7× 10³ 103 PAM 230 2/1 5.3 × 10⁹ 8.2 × 10⁻⁵ 1.2 × 10⁴ 104 PAM 510 1/1 8.2× 10⁹ 2.3 × 10⁻⁵ 4.3 × 10⁴ 105 PAM 264 1/1 2.0 × 10¹⁰ 1.9 × 10⁻⁵ 5.3 ×10⁴ 106 PAM 220 1/1 2.2 × 10¹⁰ 2.1 × 10⁻⁵ 4.8 × 10⁴ 107 PAM 285 1/2 1.4× 10¹¹ 2.5 × 10⁻⁶   4 × 10⁵ 108 PAAMPSA 260 1/0.1 2.4 × 10⁹ 1.6 × 10⁻⁴6.3 × 10³ 109 PAAMPSA 350 1/0.3 9.2 × 10⁹ 4.6 × 10⁻⁴ 2.2 × 10³ 110PAAMPSA 230 1/0.5 4.5 × 10⁸ 9.5 × 10⁻⁴ 1.1 × 10³ 111 PAAMPSA 630 1/0.53.7 × 10⁸ 4.3 × 10⁻⁴ 2.3 × 10³ 112 PAAMPSA 920 1/0.5 6.8 × 10⁷ 1.6 ×10⁻⁴ 6.3 × 10³ 113 PAAMPSA 950 1/1 2.8 × 10⁸ 3.8 × 10⁻⁴ 2.6 × 10³ 114PAAMPSA 1280  1/1 6.7 × 10⁷ 1.2 × 10⁻³ 8.3 × 10² 115 PAAMPSA 1740  1/22.5 × 10⁸ 2.3 × 10⁻⁴ 4.3 × 10³ 116 PAAMPSA 3060  1/2 8.4 × 10⁷ 3.9 ×10⁻⁴ 2.6 × 10³ 117 PEO 250 1/1 3.0 × 10⁹ 1.3 × 10⁻⁴ 7.7 × 10³

Example 9

[0079] 20 g of a PANI-PAAMPSA solution as prepared in Example 2 wasmixed (at room temperature for 12 days) with 10 g of 1 wt % PAM solutionas prepared in Example 4 and 2.0 g of 15% PAAMPSA solution (availablefrom Aldrich) The solution was then filtered through 0.45 μmpolypropylene filters. The content of PANI-PAAMPSA in the blend solutionwas 33wt % Different blend ratios of the PANI-PAAMPSA:PAAMPSA:PAM blendsolutions are prepared by changing the concentrations in the startingsolutions.

Example 10

[0080] Example 9 was repeated; the content of PANI-PAAMPSA is kept at 33wt %, but the ratio of host polymers PAAMPSA/PAM (w/w) was changed to2/0, 0.5/1, 1/1 and 0/2, respectively.

Example 11

[0081] 30 g of a solution as prepared in Example 2 was mixed with 15 gof deionized water and 0.6 g of PAM (M.W. 5,000,000-6,000,000, availablefrom Polysciences) under stirring at room temperature for 4-5 days. Theratio of PANI-PAAMPSA to PAM in the blend solution was 1/2. Blendsolutions were also prepared in which the content of PANI-PAAMPSA was 0,10, 25 and 40%, respectively.

Example 12

[0082] The resistance measurements of Example 8 were repeated, but thePANI(ES) layer was spin-cast from the blend solutions prepared inExamples 11. FIG. 3 shows the conductivity of PANI(ES)-blend films withdifferent blend compositions. As can be seen from the data, theconductivity can be controlled in wide range to meet displayrequirements. Conductivity values less than 10⁻⁵ S/cm (electricalresistivity of greater than 10⁻⁵ ohm-cm). can be obtained. With higherconcentrations of PAM in the blend, the conductivity dropped below 10⁻⁶S/cm (electrical resistivity of greater than 10⁻⁶ ohm-cm).

[0083] This Example demonstrates that PANI(ES)-blend films can beprepared with conducitivities less than 10⁻⁵ S/cm and even less than10⁻⁶ S/cm.

Example 13

[0084] The resistance measurements of Example 8 were repeated, but thePANI(ES) layer was spin-cast from the blend solutions as prepared inExamples 9 and 10. Table 2 shows the conductivity of polyblend filmswith different blend compositions; the conductivity can be controlledover a wide range of values.

[0085] This Example demonstrates that the PANI-PAAMPSA blends usingPAAMPSA/PAM as host polymers can be prepared with bulk conductivitiesless than 10⁻⁵ S/cm, even less than 10⁻⁶ S/cm and for specificformulations less than 10⁻⁷ S/cm. The conductivities of the PANI(ES)blends are sufficiently low that interpixel current leakage can belimited without need for patterning the blend film. TABLE 2 Bulk anssurface resistance for PANI(ES) blends with different compositions andthickness Ratio of host polymers* Thick- Con- PAAMPS/ ness ductivityResistivity PAM (Å) R (ohm)** ohm/sq (S/cm) (ohm-cm) 1.5/0.5 2100 9.8 ×10⁶ 5.2 × 10⁸ 9.0 × 10⁻⁵ 1.1 × 10⁴ 1000 1.0 × 10⁸ 5.3 × 10⁹ 1.9 × 10⁻⁵5.3 × 10⁴ 2/0 2080 1.6 × 10⁷ 8.5 × 10⁸ 5.6 × 10⁻⁵ 1.8 × 10⁴ 1300 3.9 ×10⁷ 2.1 × 10⁹ 3.7 × 10⁻⁵ 2.7 × 10⁴ 0.5/1   1850 1.2 × 10⁹ 6.4 × 10¹⁰ 9.3× 10⁻⁷ 1.1 × 10⁶ 1000 6.8 × 10⁹ 3.6 × 10¹¹ 2.8 × 10⁻⁷ 3.6 × 10⁶ 1/1 16201.1 × 10⁹ 5.9 × 10¹⁰ 1.0 × 10⁻⁶ 1.6 × 10⁶ 1100 2.6 × 10¹⁰ 1.4 × 10¹² 6.5× 10⁻⁸ 1.5 × 10⁷ 0/2 1200   2 × 10¹⁰ 1.0 × 10¹² 8.3 × 10⁻⁸ 1.2 × 10⁷ 750 3.4 × 10¹¹ 1.8 × 10¹³ 7.4 × 10⁻⁹ 1.4 × 10⁸

Example 14

[0086] Light emitting diodes were fabricated usingpoly(2-(3,7dimethyloctyloxy)-5-methoxy-1,4-phenylenevinylene) (DMO-PPV)as the active semiconducting, luminescent polymer; the thickness of theDMO-PPV films were 500-1000 Å. Indium/tin oxide was used as the firstlayer of the bilayer anode. PANI-PAAMPSA (of Example 2) was spin-coatedfrom 1% solution/dispersion in water onto ITO with thicknesses rangingfrom 100 to 800 Å, and thereafter, baked at 90° C. in vacuum oven for0.5 hour. The device architecture wasITO/PANI(ES)-PAAMPSA/DMO-PPV/metal. Devices were fabricated using bothITO on glass as the substrate (Applied ITO/glass) and using ITO onplastic, polyethylene terephthalate, PET, as the substrate (Courtauld'sITO/PEI); in both cases, ITO/PANI-PAAMPSA bilayer was the anode and thehole-injecting contact. Devices were made with a layer of Ba as thecathode. The metal cathode film was fabricated on top of the DMO-PPVlayer using vacuum vapor deposition at pressures below 1×10⁻⁶ Torryielding an acting layer with area of 3 cm². The deposition wasmonitored with a STM-100 thickness/rate meter, available from SyconInstruments, Inc., (East Syracuse, N.Y. 13057) 2,000 Å to 5,000 Å ofaluminum was deposited on top of the calcium layer. For each of thedevices, the current vs. voltage curve, the light vs. voltage curve, andthe quantum efficiency were measured. FIG. 4 shows the light output(curve 400) and external quantum efficiency (curve 410) ofITO/PANI(ES)-PAAMPSA/DMO-PPV/Ba device. The external efficiency of thedevice with bilayer PANI(ES)-PAAPMSA/ITO anode is significantly higherthan device with ITO anode.

[0087] This Example demonstrates that high performance polymer LEDs canbe fabricated using PANI-PAAMPSA as the second layer of the bilayeranode.

Example 15

[0088] The resistance measurements of Example 8 were repeated usingcommercially available poly(ethylenedioxythiophene), PEDT, polyblendsolutions available from Bayer AG (Pittsburgh, Pa. 15205). Table 3 showsthat the PANI(ES) blends prepared by this invention (see EXAMPLE 9)yield a layer with much lower conductivity than that obtained from PEDT.This Example demonstrates that the conductivity of PEDT is too high tobe used in passively addressed pixelated displays; the inter-pixelleakage current will lead to cross-talk and to reduced efficiency. TABLE3 Thickness and conductivity of new PEDT-PSS in comparison with PANI(ES)blend Thickness R* Rs Conductivity Resistivity Type Spin speed (RPM) (Å)(Mohm) (Mohm/sq) (S/cm) (ohm-cm) PEDT-PSS 600 2800 0.22 11.7 3.0 × 10⁻³3.3 × 10² 800 2500 0.31 16.5 2.4 × 10⁻³ 4.2 × 10² 1000 2000 0.33 17.02.9 × 10⁻³ 3.4 × 10² 1400 1700 0.38 19.4 3.0 × 10⁻³ 3.3 × 10² 2000 13300.57 30.4 2.5 × 10⁻³ 4.0 × 10² 4000 1000 0.77 41.0 2.4 × 10⁻³ 4.2 × 10²PEDT-TSS 600 1000 0.16 8.5 1.2 × 10⁻² 8.3 × 10¹ 1000 760 0.19 10.1 1.3 ×10⁻² 7.7 × 10¹ PANI(ES) 1000 2100 9.8 522 9.0 × 10⁻⁵ 1.1 × 10⁴ blend2000 1500 29.0 1550 4.3 × 10⁻⁵ 2.3 × 10⁴ 3000 1200 84.0 4480 1.9 × 10⁻⁵5.3 × 10⁴ 4000 1000 100.0 5300 1.9 × 10⁻⁵ 5.3 × 10⁴

Example 16

[0089] Example 5 was repeated, but the host polymer was, respectively,poly(acrylic acid), PAM-carboxy, polyvinylpyrrolidone and polystyrene(aqueous emulsion) instead of PAM. PANI-PAAMPSA/hostpolymersolution/dispersion was prepared as indicated in Example 5.

Example 17

[0090] The device measurements summarized in Example 14 were repeated,but the PANI(ES)-blend layer was spin-cast from the blend solutions asprepared in Examples 5 and 16. Table 4 shows the device performance ofLEDs fabricated from polyblend films with different host polymers.

[0091] This Example demonstrates that the use of PANI-PAAMPSA blends canbe used to fabricate polymer LEDs with significantly higher efficiency;this higher efficiency is obtained because inter-pixel current leakagehas been significantly reduced by using the high resistancePANI(ES)-blend as the hole injection layer. TABLE 4 Performance ofdevices fabricated with different PANI(ES) blends# Performance at 8.3mA/cm²* Host polymer V QE(%) cd/A Lm/W PAM(300Å) 4.9 3.5 6.3 4.1PAM(2000Å)** 4.3 3.1 4.5 3.3 poly(acrylic acid)(300Å) 4.4 3.7 7.0 5.0PAM-carboxy — — — 0.04 polyvinylpyrrolidone 6.3 1.0 1.3 0.6polystyrene(aq. emulsion) 6.1 0.6 0.8 0.4

Example 18

[0092] The device measurements summarized in Example 14 were repeated,but the PANI(ES) layer was spin-cast from the blend solutions withdifferent PANI(ES)PAAMPSA/PAM ratios (see EXAMPLE 11). Table 5 shows thedevice performance of LEDs fabricated from polyblend films withdifferent PANI-PAAMPSA/PAM ratios.

[0093] The higher efficiency correlates well with higher resistance inthe PANI(ES)(ES)-blend layer. The higher efficiency is obtained with thehigher resistance in the PANI(ES)(ES)-blend layer because there is nowasted current due to inter-pixel current leakage. TABLE 5 Performanceof devices fabricated different PANI(ES) blends# PANI(ES)PAAMPSA/PAMPerformance at 8.3 mA/cm² (w/w) V QE(%) cd/A Lm/W 1/9 9.1 5.0 10.7 3.71/3 5.6 5.0 12.6 7.1 1/2 5.2 4.9 13.0 7.8   1/1.5 5.2 4.8 12.1 7.3 1/04.6 4.4 11.6 8.0

Example 19

[0094] The device measurements summarized in Example 14 were repeated,but poly[5-(4-(3,7-dimethyloctyloxy)phenyl)-phenylene-1,4-vinylene](DMOP-PPV) and its random co-polymer with DMO-PPV were used instead ofDMO-PPV. The device performance data are listed in Table 6.

[0095] This EXAMPLE demonstrates that different color (e.g. red, green,orange etc) can be fabricated using PANI-PAAMPSA as the hole injectionlayer. TABLE 6 Device performance of different luminescent polymer onPANT(ES)-PAAMPSA electrode Polymer Composition EL peak (DMOP-PPV)_(n)-position Device performance* DMO-PPV)_(m) V luminance efficiency n m(nm) (V) (cd/m2) (%) color 100 0 510 5.3 47 1.2 green 98 2 530 4.8 1303.2 yellowish- green 50 50 580 6.6 198 4.9 orange 0 100 610 3.3 160 3.9red

Example 20

[0096] The device of Example 14 was encapsulated using a cover glasssandwiched by UV curable epoxy. The encapsulated devices were run at aconstant current of 8.3 mA/cm² in ambient atmosphere in an oven attemperatures 25, 50, 70 and 85° C. The total current through the deviceswas 25 mA with luminance of approximately approximately 100 cd/cm². FIG.5 shows the light output (curve 510) and voltage increase (curve 512)during operation at 85° C. In contrast to devices with ITO as anode,which degrade within 10-20 hours of stress at 85° C., the half life ofthe devices with the ITO/PAAMPSA bilayer exceeds 450 hours with a verylow vohage increase (5 mV/hour). From Ahrennius plots of the luminancedecay and voltage increase data collected at 50, 70 and 85° C., thetemperature acceleration factor was estimated to be ca. 100. Thus, theextrapolated stress life at room temperature was determined to beapproximately 40,000 hours.

[0097]FIG. 6 shows the real time stress data at room temperature lightoutput (curve 600) and voltage increase (curve 610) at the operation at25° C. As can be seen in FIG. 6, after 10,000 hours stress, the lightoutput has decreased by only approximately 10%. The voltage increase isless than 0.15 mV/hour.

[0098] This Example demonstrates that long lifetime can be obtained forpolymer LEDS fabricated with high resistance PANI(ES) layers.

Example 21

[0099] Examples 14 and 20 were repeated, but the higher resistancePANI(ES) PAAMPSA blend (Example 9) was used for the holeinjection/layer. FIG. 7 shows the luminance (curve 700) and voltage (atconstant current) (curve 710) vs time during stress at 16.5 mA/cm2 withthe device at 70° C.

[0100] This Example demonstrates that long lifetime, high performancedisplays can be fabricated using the PANI-PAAMPSA/PAM blend as holeinjection layer.

Example 22

[0101] Example 1 was repeated, but 1.7 g of PAM (Polysciences, M.W.4-6M) was added into aniline-PAAMPSA-water mixture. After vigorousstirring and complete dissolution of PAM in the reaction mixture theoxidant was added into reaction mixture. All other steps were the sameas Example 1. A PANI(ES)-blend with polyaniline to PAM ratio of 1:2 wasprepared directly from polymerization. Aqueous solutions/dispersions(for example, 1 or 2% w/w) of the final product were prepared bystirring of the resulting powder in deionized water at room temperaturefor 24 hours in a plastic container. The solution was filtered through a0.45 μm filter. The bulk conductivity of a thin film spin-cast from theresulting aqueous dispersion was measured to be (approximately 10⁻⁶S/cm); i.e. three orders of magnitude lower than the film from Example 1of same thickness; and one order of magnitude lower than that of blendprepared by mixing of aqueous dispersion from Example 1 and PAM solutionin water (see Example 5).

[0102] This Example demonstrates that the desired high resistancePANI(ES)-PAAMPSA/PAM blend can be synthesized directly in a singleprocess.

Example 23

[0103] Three passively addressed displays were fabricated, each with 96rows and 64 columns. The gap between ITO columns was 50 μm. A singlepixel was addressed in each display. Photographs of the resultingemission are displayed in FIG. 8. The three displays were identical inevery respect except for the resisitivity of the material used for thehole injection layer. The display in FIG. 8a had a low resistance PEDTlayer (resistivity approximately equal to 200 ohm-cm) such that theresistance between columns was approximately 20,000 ohms. The display inFIG. 8b had a PANI(ES) polyblend layer (resistivity approximately equalto 4,000 ohm-cm) such that the resistance between columns wasapproximately 400,000 ohms. The display in FIG. 8c had a higherresistance PANI(ES) polyblend layer (resistivity approximately equal to50,000 ohm-cm) such that the resistance between columns wasapproximately 5,000,000 ohms.

[0104] As demonstrated in FIG. 8a, with 20,000 ohms between columns,there is significant cross-talk. This cross-talk had two implications:

[0105] (i) The resolution and clarity of the display (FIG. 8a) waslimited by the cross-talk. Note that the display in FIG. 8b is improvedcompared to FIG. 8a and the display in FIG. 8c does not exhibit thecross-talk problem.

[0106] (ii) The efficiency of the display (FIGS. 8a and 8 b) was reducedby the inter-pixel leakage current.

[0107] The lower efficiency means that the display required more powerthan that required in the identical display (FIG. 8c) where thecross-talk was negligible. Because of inter-pixel current leakage, thedisplay shown in FIG. 8a had an efficiency of approximately half that ofthe display shown in FIG. 8c. The reduction in efficiency due tointer-pixel leakage current can be a factor as large 3-5 times dependingon the detailed inter-pixel spacing and pixel size. Using these data, itwas estimated that displays fabricated with a PANI(ES) polyblend layerwith resistivity in range from 10⁴ ohm-cm to 10⁵ ohm-cm will not besubject to reduced efficiency from inter-pixel leakage current.

[0108] This Example demonstrates the importance of using high resistancePANI(ES) polyblend for the hole injection layer in passively addressedpolymer LED displays.

What is claimed is:
 1. A PANI-PAAMPSA film comprising polyaniline in theemeraldine salt form (PANI) with poly(2-acrylamido-2methyl-1-propanesulfonic acid) (PAAMPSA) as a counterion.
 2. The film ofclaim 1, having an electrical resistivity greater than 10² ohm-cm. 3.The film of claim 1, further comprising at least one water-soluble hostpolymer.
 4. The film of claim 3, wherein the water-soluble host polymeris polyacrylamide (PAM), PAAMPSA, poly(acrylic acid) (PAA),poly(styrenesulfonic acid), poly(vinyl pyrrolidone)(PVPd), acrylamidecopolymers, cellulose derivatives, carboxyvinyl polymer, poly(ethyleneglycols), poly(ethylene oxide) (PEO), poly(vinyl alcohol) (PVA),poly(vinyl methyl ether), polyamine, polyimines, polyvinylpyridines,polysaccharide, polyurethane dispersion, and combinations thereof.
 5. Amethod of forming the film of claim 1, comprising the steps of:providing a substrate; providing an aqueous dispersion/solutioncomprising PANI-PAAMPSA; and depositing the aqueous dispersion/solutiononto the substrate to form the film.
 6. The method of claim 5, whereinthe aqueous dispersion/solution further comprises at least onewater-soluble host polymer.
 7. The method of claim 5, wherein thewater-soluble host polymer is polyacrylamide (PAM), PAAMPSA,poly(acrylic acid) (PAA), poly(styrenesulfonic acid), poly(vinylpyrrolidone)(PVPd), acrylamide copolymers, cellulose derivatives,carboxyvinyl polymer, poly(ethylene glycols), poly(ethylene oxide)(PEO), poly(vinyl alcohol) (PVA), poly(vinyl methyl ether), polyamine,polyimines, polyvinylpyridines, polysaccharide, polyurethane dispersion,and combinations thereof.
 8. An electronic device comprising aPANI-PAAMPSA film comprising polyaniline in the emeraldine salt form(PANI) with poly(2-acrylamido-2 methyl-1-propanesulfonic acid) (PAAMPSA)as a counterion.
 9. The electronic device of claim 8, wherein the filmhas an electrical resistivity greater than 10² ohm-cm.
 10. Theelectronic device of claim 8, wherein the film further comprises atleast one water-soluble host polymer.
 11. The electronic device of claim10, wherein the at least one water-soluble host polymer ispolyacrylamide (PAM), PAAMPSA, poly(acrylic acid) (PAA),poly(styrenesulfonic acid), poly(vinyl pyrrolidone)(PVPd), acrylamidecopolymers, cellulose derivatives, carboxyvinyl polymer, poly(ethyleneglycols), poly(ethylene oxide) (PEO), poly(vinyl alcohol) (PVA),poly(vinyl methyl ether), polyamine, polyimines, polyvinylpyridines,polysaccharide, polyurethane dispersion, and combinations thereof. 12.The electronic device of claim 11, wherein the film has an electricalresistivity greater than 10⁴ ohm-cm.
 13. A light-emitting diodecomprising a PANI-PAAMPSA film comprising polyaniline in the emeraldinesalt form (PANI) with poly(2-acrylamido-2 methyl-1-propanesulfonic acid)(PAAMPSA) as a counterion.
 14. The light-emitting diode of claim 13,wherein the film has an electrical resistivity greater than 10² ohm-cm.15. The device of claim 13, wherein the film further comprises at leastone water-soluble host polymer.
 16. The device of claim 15, where in theat least one water-soluble host polymer is polyacrylamide (PAM),PAAMPSA, poly(acrylic acid) (PAA), poly(styrenesulfonic acid),poly(vinyl pyrrolidone)(PVPd), acrylamide copolymers, cellulosederivatives, carboxyvinyl polymer, poly(ethylene glycols), poly(ethyleneoxide) (PEO), poly(vinyl alcohol) (PVA), poly(vinyl methyl ether),polyamine, polyimines, polyvinylpyridines, polysaccharide, polyurethanedispersion, and combinations thereof.
 17. The device of claim 16,wherein the film has an electrical resistivity greater than 10⁴ ohm-cm.18 The device of claim 16, wherein the film has an electricalresistivity of greater than 10⁵ ohm-cm.
 19. The device of claim 13,wherein the film is disposed between a light-emitting polymer and a highwork function electrode.
 20. The device of claim 19, wherein: the highwork function electrode comprises polyaniline, PEDT, indium tin oxide,an oxide of a metal from Group IIA (Be, Mg, Ca, Sr, Ba, Ra), an oxide ofother metals from Groups IIIA (B, Al, Ga, Tl) or an oxide of metals fromGroup IVA (C, Si, Ge, Sn, Pb); and wherein the device further comprisesa low work function electrode selected from alkaline earth metals,alloys of alkaline earth metals, and alkaline earth metal oxides.